1. Field of the Invention
This invention relates generally to improvements in gas turbine engines and, more particularly, to improvements in sealing the annular gas chambers which retain turbine cooling air against parasitic leakage.
2. Description of the Prior Art
It is a common practice in gas turbine engines to use a portion of the compressor discharge for engine cooling. A portion of the air used for this purpose is directed to a gas accelerator, well known in the art, which accelerates the air through a pressure decrease and swirls it in the direction of enginge rotation. The swirled gases are discharged into an annular chamber. In addition to receiving the swirled cooling air, this chamber may also be used in the manner well known in the art to provide a balancing force on the engine, in which case it may be referred to as the balance piston chamber. The chamber is sealed from adjacent areas of differing pressure by a system of gas seals placed at the junctures between rotating and stationary elements within the chamber. Gas seals outside the chamber have also been used to further minimize airflow between the chamber and adjacent areas of differing pressure.
Gas seals, as herein contemplated, are of the labyrinth type, comprising one or more circumferential teeth on one part which are contiguous with a circumferential sealing surface on another part, with the two parts or elements being relatively rotatable. Such a seal provides a high restriction to gas flow and has the further advantage of permitting rotation between the two parts of the seal. This type of seal has many other well known advantages and is widely used in gas turbin engines.
A disadvantage of seals of this type is that they are subject to parasitic leakage in the direction of decreasing pressure. When such seals are used to retain cooling air for high temperature gas turbines, such leakage is particularly undesirable since it reduces the thermodynamic efficiency of the engine.
Heretofore it has been the practice to direct the leakage of the individual gas seals separately in a parallel fashion to adjacent areas of lower pressure. The total leakage of such systems is the combined leakage of all the seals present in the system.
It is the object of the present invention to improve the thermodynamic efficiency of gas turbine engines by reducng the total leakage of the gas seals used to retain turbine cooling air.